U.S. officials suspect that Libyan leader Moammar Gadhafi, using the cover of Palestinian and Japanese terrorist groups, is a major instigator of a sudden resurgence in terrorist attacks on American and Western targets in the Middle East and elsewhere.

"The general assessment here is that the Libyans are becoming more active," said L. Paul Bremer III, the State Department's chief antiterrorist expert.

The main suspected Libyan surrogate today appears to be Sabry Banna, the most notorious Palestinian terrorist and better known as Abu Nidal, U.S. antiterrorist officials said. After being expelled from Syria last summer, he has set up his headquarters in Tripoli, the Libyan capital.

U.S. antiterrorist officials also strongly suspect that Gadhafi has enlisted the services of the Japanese Red Army terrorist organization to carry out operations against U.S. and other Western targets.

These officials conceded that the evidence of a direct connection between Libya and the two terrorist groups is largely circumstantial and that there is still no proof, or "smoking gun," to show Gadhafi is masterminding the new outbreak of terrorist incidents. There is debate, and no agreement, in the administration over the extent of Gadhafi's role, according to one official.

But U.S. intelligence agencies have concluded that Abu Nidal and Red Army operatives have been responsible for a number of recent terrorist incidents around the world. Some antiterrorist officials such as Bremer believe they had Gadhafi's blessing, if not his direction, because they coincided so closely with the second anniversary of the April 14-15, 1986, U.S. retaliatory air raid on Gadhafi's personal living quarters and other targets in Tripoli.

The U.S action was in retaliation for the bombing of a West Berlin disco earlier that month that killed a U.S. army sergeant and wounded several others.

Terrorist incidents this year during the April 10-15 period included four attacks on U.S. Information Agency buildings in three Latin American countries and a bomb attack on the USO club in Naples, Italy. U.S. antiterrorist officials said there is still no hard evidence of Libyan involvement in the attacks in Costa Rica, Colombia and Peru but they remain suspicious because of the timing.

However, the officials said there is considerable evidence that the Japanese Red Army was responsible for the Naples bombing April 14 in which five persons, including a U.S. servicewoman, were killed, and 15 others, including four U.S. sailors, injured. A Japanese Red Army member, Junzo Okudaira, is wanted in connection with the incident, which Italian authorities also suspect was in retaliation for the U.S. raid on Tripoli because of the coincidence of dates.

Another suspected Japanese Red Army member, Yu Kikumura, was arrested April 12 on the New Jersey Turnpike after he was found carrying three homemade bombs in his car. Police have not been able to determine what he intended to do with the bombs.

The spate of terrorist incidents has not let up. On May 10, a bomb went off at the Citibank office in New Delhi. U.S. officials believe this also was a Japanese Red Army operation.

On May 15 in Khartoum, three Arabs with Lebanese passports attacked the Acropol Hotel and British Club with machineguns and grenades, killing a British family of four and three other persons, and injuring 21, including two Americans. The three Arabs confessed to Sudanese police that they belong to the Abu Nidal organization, according to Sudanese press reports.

Signs of Gadhafi's new activism in terrorist and subversive activities are worldwide and go back at least to late last fall, U.S. antiterrorist officials said.

They noted the interception by French authorities in early November of a ship carrying 150 tons of Libyan-provided arms, including surface-to-air missiles, bound for the Irish Republican Army. At the time, State Department spokesman Charles E. Redman called the haul "the largest terrorist arms shipment ever intercepted."

On Feb. 20, two Libyan agents found in possession of bomb-making materials were arrested at the West African airport in Dakar, Senegal. They had come from Cotonou, Benin, where they were in contact with the Libyan "People Bureau," as Libya calls its embassies.

On March 25, a Lebanese attacked an Alitalia crew shuttle bus at the airport in Bombay, India, firing a gun and hurling two grenades that failed to detonate. U.S. officials believe the attacker mistakenly thought the bus had Pan American crew members aboard. They also believe, on the basis of the weapons used, that he was an Abu Nidal operative.

Some U.S. antiterrorist officials also believe Libya may have had at least an indirect hand in antigovernment demonstrations May 16 on the South Pacific island of Vanuatu. They note reports that Libya trained some supporters of the opposition leader, Tourism Minister Barak Sope, who organized the street distubances.

Bremer said Gadhafi's apparent reengagement in terrorist activities has come at a time when he also appears to be successfully overcoming the pariah status imposed on him by the United States and other Western nations following his involvement in a spate of terrorist incidents in early 1986.

Gadhafi's relations with Turkey and Tunisia, both close U.S. allies, have improved noticeably over the past few months and the number of West Europeans working in Libya is "creeping back up," according to U.S. officials.

Bremer said he fears there is now "a drift" in Western resolve to keep Qadhafi isolated and under both political and economic pressure to end his involvement in terrorist activities.

But U.S. antiterrorist experts said that in addition to Gadhafi and Abu Nidal, they are worried by accusations from Palestine Liberation Organization Chairman Yasser Arafat and other top PLO officials of U.S. complicity in the suspected Israeli assassination of PLO leader Khalil Wazir (Abu Jihad) in Tunis April 16.

The State Department has sent messages through various Arab diplomatic channels vehemently denying any U.S. involvement in the attack and warning Arafat to desist in his accusations. This unusual action was taken because the administration fears Arafat's repeated accusation will stir PLO radicals to terrorist attacks on U.S. interests in retaliation.

But at a news conference May 23 in Tunis, the PLO leader charged the United States had given Israel advance approval for its commando raid on Abu Jihad's house outside Tunis and accused Washington of supporting "institutionalized Israeli terrorism" against his organization.